Methods for fabricating and using nanowires

ABSTRACT

Methods, apparatuses, systems, and devices relating to fabricating one or more nanowires are disclosed. One method for fabricating a nanowire includes: selecting a particular wavelength of electromagnetic radiation for absorption for a nanowire; determining a diameter corresponding to the particular wavelength; and fabricating a nanowire having the determined diameter. According to another embodiment, one or more nanowires may be fabricated in an array, each having the same or different determined diameters. An image sensor and method of imaging using such an array are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/966,514, filed Dec. 13, 2010 and claims the benefit of U.S.Provisional Application No. 61/357,429, filed on Jun. 22, 2010, which ishereby incorporated by reference as if fully set forth herein.

This application is related to the disclosures of U.S. patentapplication Ser. No. 12/204,686, filed Sep. 4, 2008 (now U.S. Pat. No.7,646,943, issued Jan. 12, 2010), Ser. No. 12/648,942, filed Dec. 29,2009 (now U.S. Pat. No. 8,229,255, issued Jul. 24, 2012), Ser. No.13/556,041, filed Jul. 23, 2012, Ser. No. 15/057,153, filed Mar. 1,2016, Ser. No. 12/270,233, filed Nov. 13, 2008 (now U.S. Pat. No.8,274,039, issued Sep. 25, 2012), Ser. No. 13/925,429, filed Jun. 24,2013 (now U.S. Pat. No. 9,304,035, issued Apr. 5, 2016), Ser. No.15/090,155, filed Apr. 4, 2016, Ser. No. 13/570,027, filed Aug. 8, 2012(now U.S. Pat. No. 8,471,190, issued Jun. 25, 2013), Ser. No.12/472,264, filed May 26, 2009 (now U.S. Pat. No. 8,269,985, issued Sep.18, 2012), Ser. No. 13/621,607, filed Sep. 17, 2012 (now U.S. Pat. No.8,514,411, issued Aug. 20, 2013), Ser. No. 13/971,523, filed Aug. 20,2013 (now U.S. Pat. No. 8,810,808, issued Aug. 19, 2014), Ser. No.14/459,398 filed Aug. 14, 2014, Ser. No. 12/472,271, filed May 26, 2009(now abandoned), Ser. No. 12/478,598, filed Jun. 4, 2009 (now U.S. Pat.No. 8,546,742, issued Oct. 1, 2013), Ser. No. 14/021,672, filed Sep. 9,2013 (now U.S. Pat. No. 9,177,985, issued Nov. 3, 2015), Ser. No.12/573,582, filed Oct. 5, 2009 (now U.S. Pat. No. 8,791,470, issued Jul.29, 2014), Ser. No. 14/274,448, filed May 9, 2014, Ser. No. 12/575,221,filed Oct. 7, 2009 (now U.S. Pat. No. 8,384,007, issued Feb. 26, 2013),Ser. No. 12/633,323, filed Dec. 8, 2009 (now U.S. Pat. No. 8,735,797,issued May 27, 2014), Ser. No. 14/068,864, filed Oct. 31, 2013 (now U.S.Pat. No. 9,263,613, issued Feb. 16, 2016), Ser. No. 14/281,108, filedMay 19, 2014 (now U.S. Pat. No. 9,123,841, issued Sep. 1, 2015), Ser.No. 13/494,661, filed Jun. 12, 2012 (now U.S. Pat. No. 8,754,359, issuedJun. 17, 2014), Ser. No. 12/633,318, filed Dec. 8, 2009 (now U.S. Pat.No. 8,519,379, issued Aug. 27, 2013), Ser. No. 13/975,553, filed Aug.26, 2013 (now U.S. Pat. No. 8,710,488, issued Apr. 29, 2014), Ser. No.12/633,313, filed Dec. 8, 2009, Ser. No. 12/633,305, filed Dec. 8, 2009(now U.S. Pat. No. 8,299,472, issued Oct. 30, 2012), Ser. No.13/543,556, filed Jul. 6, 2012 (now U.S. Pat. No. 8,766,272, issued Jul.1, 2014), Ser. No. 14/293,164, filed Jun. 2, 2014, Ser. No. 12/621,497,filed Nov. 19, 2009 (now abandoned), Ser. No. 12/633,297, filed Dec. 8,2009 (now U.S. Pat. No. 8,889,455, issued Nov. 18, 2014), Ser. No.14/501,983 filed Sep. 30, 2014, 12/982,269, filed Dec. 30, 2010 (nowU.S. Pat. No. 9,299,866, issued Mar. 29, 2016), Ser. No. 15/082,514,filed Mar. 28, 2016, 12/966,573, filed Dec. 13, 2010 (now U.S. Pat. No.8,866,065, issued Oct. 21, 2014), Ser. No. 14/503,598, filed Oct. 1,2014, Ser. No. 12/967,880, filed Dec. 14, 2010 (now U.S. Pat. No.8,748,799, issued Jun. 10, 2014), Ser. No. 14/291,888, filed May 30,2014, Ser. No. 12/974,499, filed Dec. 21, 2010 (now U.S. Pat. No.8,507,840, issued Aug. 13, 2013), Ser. No. 12/966,535, filed Dec. 13,2010 (now U.S. Pat. No. 8,890,271, issued Nov. 18, 2014) Ser. No.12/910,664, filed Oct. 22, 2010 (now U.S. Pat. No. 9,000,353, issuedApr. 17, 2015), Ser. No. 14/632,739, filed Feb. 26, 2015, Ser. No.12/945,492, filed Nov. 12, 2010, Ser. No. 13/047,392, filed Mar. 14,2011 (now U.S. Pat. No. 8,835,831, issued Sep. 16, 2014), Ser. No.14/450,812, filed Aug. 4, 2014, Ser. No. 13/048,635, filed Mar. 15, 2011(now U.S. Pat. No. 8,835,905, issued Sep. 16, 2014), Ser. No.14/487,375, filed Sep. 16, 2014 (now U.S. Pat. No. 9,054,008, issuedJun. 9, 2015), Ser. No. 14/705,380, filed May 6, 2015, Ser. No.13/106,851, filed May 12, 2011 (now U.S. Pat. No. 9,082,673, issued Jul.14, 2015) Ser. No. 14/704,143, filed May 5, 2015, Ser. No. 13/288,131,filed Nov. 3, 2011, Ser. No. 14/334,848, filed Jul. 18, 2014, Ser. No.14/032,166, filed Sep. 19, 2013, Ser. No. 13/543,307, filed Jul. 6,2012, Ser. No. 13/963,847, filed Aug. 9, 2013, Ser. No. 15/093,928,filed Apr. 8, 2016, Ser. No. 13/693,207, filed Dec. 4, 2012, 61/869,727,filed Aug. 25, 2013, Ser. No. 14/322,503, filed July. 2, 2014, Ser. No.14/311,954, filed Jun. 23, 2014, Ser. No. 14/563,781, filed Dec. 8,2014, 61/968,816, filed Mar. 21, 2014, Ser. No. 14/516,402, filed Oct.16, 2014, Ser. No. 14/516,162, filed Oct. 16, 2014, 62/161,485, filedMay 14, 2015 and 62/307,018, filed Mar. 11, 2016 are each herebyincorporated by reference in their entirety.

FIELD

This application generally relates to semiconductor sensing devices andmanufacturing, and in particular, selected spectral absorption ofnanowires.

BACKGROUND

An image sensor may be fabricated to have a large number of identicalsensor elements (pixels), generally more than 1 million, in a(Cartesian) square grid. The pixels may be photodiodes, or otherphotosensitive elements, that are adapted to convert electromagneticradiation into electrical signals. Recent advances in semiconductortechnologies have enabled the fabrication of nanoscale semiconductorcomponents such as nanowires.

Nanowires have been introduced into solid state image devices to confineand transmit electromagnetic radiation impinging thereupon to thephotosensitive elements. These nanowires can be fabricated from bulksilicon which appears gray in color, although researchers have patternedthe surface of silicon so it “looks” black and does not reflect anyvisible light.

However, nanowires configured to selectively absorb (or to lower thereflectance of) light at a predetermined wavelength have not beenfabricated.

SUMMARY

According to an embodiment, a method for fabricating a nanowirecomprises: selecting a particular wavelength of electromagneticradiation for absorption for a nanowire; determining a diametercorresponding to the particular wavelength; and fabricating a nanowirehaving the determined diameter.

According to an embodiment, there may be a nearly linear relationshipbetween the nanowire diameter and the wavelength of electromagneticradiation absorbed by the nanowire. However, it will be appreciated thatother relationships may exists, based on the nanowire materials,fabrication techniques, cross-sectional shape, and/or other parameters.Based on the diameter of the nanowire, the particular wavelength oflight absorbed may be within the UV, VIS or IR spectra.

According to an embodiment, the nanowire may be fabricated to have adiameter between about 90 and 150 nm for absorbing a wavelength ofvisible light. Of course, the nanowire diameters may need to be smallerfor absorbing wavelengths of UV light or larger for absorbingwavelengths of IR light. While this disclosure primarily describesnanowires having a circular cross-sectional shape, it will appreciatedthat other cross-sectional shapes are also possible (e.g., those thatfunction as a waveguide).

According to an embodiment, the length of the nanowire may be, forexample, between about 1 and 10 μm (or perhaps even longer). The longerthe nanowire is, the greater the volume may be available for absorptionof electromagnetic energy.

According to an embodiment, the nanowire may be fabricated by a dryetching process, or a vapor-liquid-solid (VLS) method from a silicon orindium arsenide wafer. It will be appreciated, though, that othermaterials and fabrication techniques may also be used. Duringfabrication of the nanowire, a mask having the diameter of the nanowiremay be used to form the nanowire having substantially the same diameter.

According to an embodiment, a plurality of nanowires may be fabricatedinto an array, each having the same or different determined diameters.The size of the array may be about 100 μm×100 μm or larger. And thenanowires can be spaced at a pitch of about 1 μm or less in the x- andy- directions (Cartesian). In one implementation, the array may includeabout 10,000 or more nanowires.

According to an embodiment, the spacing (pitch) of the nanowires mayaffect the amount of absorption. For instance, near total absorption maybe realized by adjusting the spacing.

According to an embodiment, an image sensor comprises: a plurality ofpixels, each of the pixels including at least one nanowire, wherein eachof the nanowires has a diameter that corresponds to a predeterminedwavelength of electromagnetic radiation for absorption by the sensor.The pixels may include one or more nanowires having the same ordifferent determined diameters. The latter configuration may beeffective for detecting absorbing multiple wavelengths ofelectromagnetic radiation (light). For instance, a red-green-blue (RGB)pixel for an image sensor may be fabricated having three nanowireshaving different diameters configured to absorb red, green and bluelight, respectively.

According to an embodiment, the image sensor may include variouselements, such as, foreoptics configured to receive the electromagneticradiation and focus or collimate the received radiation onto the one ormore pixels, a readout circuit configured to receive output from the oneor more pixels, a processor configured to receive the output from thereadout circuit and generate an image, and a display device configuredto display the image generated by the processor. In someimplementations, the image sensor may be configured as aspectrophotometer or as a photovoltaic cell.

According to an embodiment, a method of imaging comprises: receivingelectromagnetic radiation; selectively absorbing, via one or morenanowires, at least one predetermined wavelength of electromagneticradiation, wherein each of the nanowires has a diameter corresponding toat least one predetermined wavelength of electromagnetic radiation forabsorption. The method may be used for performing multispectral imagingor hyperspectral imaging.

Other features of one or more embodiments of this disclosure will seemapparent from the following detailed description, and accompanyingdrawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure will now be disclosed, by way ofexample only, with reference to the accompanying schematic drawings inwhich corresponding reference symbols indicate corresponding parts, inwhich:

FIGS. 1A-1G are scanning electron microscope (SEM) images showingnanowire arrays of various diameters, according to an embodiment.

FIG. 2 shows a plot of reflection for silicon nanowires having differentdiameters, but having the same pitch, according to an embodiment.

FIGS. 3A-3C show experimental and simulation results for reflection ofsilicon nanowire arrays, according to an embodiment

FIG. 4 shows a plot of absorption spectra of silicon nanowire arrays,according to an embodiment.

FIG. 5 shows a plot of reflection spectra of silicon nanowire arrays,according to an embodiment.

FIG. 6 shows a plot of absorption spectra of silicon nanowire arrays,according to an embodiment.

FIG. 7 shows a plot of absorption and reflection spectra of siliconnanowire arrays, according to an embodiment.

FIG. 8 shows an exemplary dry etch method for fabricating an array ofvertical nanowires, according to an embodiment.

FIG. 9 shows an exemplary vapor liquid solid method for fabricating anarray of vertical nanowires, according to an embodiment.

FIG. 10 shows a schematic of an image sensor, according to anembodiment.

FIG. 11 shows a method for selectively imaging, according to anembodiment.

FIG. 12 shows an exemplary pixel of an image sensor formed of threenanowires having different diameters configured to absorb red, green,and blue light, respectively, according to an embodiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part thereof. In the drawings,similar symbols typically identify similar components, unless thecontext dictates otherwise. The illustrative embodiments described inthe detail description, drawings, and claims are not meant to belimiting. Other embodiments may be utilized, and other changes may bemade, without departing from the spirit or scope of the subject matterpresented here.

This disclosure is drawn to, among other things, methods, apparatuses,systems, and devices relating to the fabrication of one or morenanowires. Each of the nanowires may be fabricated to absorb (or tosignificantly lower reflectance of) a specific wavelength ofelectromagnetic radiation (light). This absorbed light includes awavelength of light in one of the ultraviolet (UV), visible (VIS) orinfrared (IR) spectra.

Silicon-based nanowires may be used for VIS applications. Verticallyaligned crystalline silicon (Si) nanowire arrays may be fabricated, invarious one embodiments, for example, by a dry etching process (as shownin FIG. 8 and further discussed below), or a Vapor Liquid Solid (VLS)growth method (as shown in FIG. 9 and further discussed below), with asilicon wafer as the starting material.

Of course, it will be appreciated that other materials and/orfabrication techniques may also be used for fabricating the nanowires inkeeping with the scope of the invention. For instance, nanowiresfabricated from an indium arsenide (InAs) wafer or related materialscould be used for IR applications.

Each nanowire can include a photodiode detector element that may form apixel in an image sensor. For example, a silicon-on-insulator (SOI)-typewafer or silicon-on-glass (SG) wafer may be used as the substratematerial for which one or more nanowires may be formed upon. Dependingon its configuration, the nanowire may be fabricated, such that: (i) thesubstrate may have an intrinsic epitaxial (epi) layer and a thin n+layer at the oxide interface; (ii) the substrate may have a lightlydoped n epi layer and a thin n+ layer at the oxide interface. (iii) thesubstrate may have lightly doped p epi layer and a thin p+ layer at theoxide interface, or (iv) the substrate may have an intrinsic epi layerand a thin p+ layer at the oxide interface.

P+ or n+ ion implantation may be employed to form a shallow junction atthe top layer of the SOI or SG wafer. As a result, the verticalstructure of p-i-n, p-n, n-i-p, n-p diode is formed respectively,depending on the substrate doping profile. In some instances, one ormore transistors may be formed on the wafer for controlling thephotocharge transfer from the nanowire to a readout circuit (ROC) and/orother electronics.

According to an aspect of the disclosure, the inventors have discovereda unique correlation between the nanowire diameter and its absorption(or reflectance) characteristics. For instance, the reflection spectraof fabricated silicon nanowire arrays each show a spectral dip forreflectance (or peak for absorption) at a specific wavelength positiondependent on the nanowire diameter.

While the experiments performed by the inventors used nanowiresfabricated having a circular cross-section, it is believed that thecross-section shape of the nanowire could be any polygonal shape, inkeeping with the scope of the invention. The nanowire may be any“waveguide” shape, although the shape might have some impact onwavelength absorption.

Also, with different nanowire spacing (pitch), absorption intensityselectivity can be realized. For instance, by adjusting the spacing ofadjacent nanowire, near total absorption may be realized.

The nanowire diameter may be determined by the diameter of a mask usedin the process by which the nanowires are fabricated. In oneimplementation, the mask be formed of aluminum (Al). Of course, it willbe appreciated that other mask materials can also be used.

A filtering effect can be employed in image sensor devices based onnanowire diameters. For instance, one or more nanowire arrays may beused to selectively absorb electromagnetic radiation (light) at aparticular wavelength. While the incident light may be white (or othercolors), absorption is “selected” by the size and/or arrangement of thenanowires. For example, the individual nanowires of the array may befabricated to absorb light of one or more particular colors in the VISspectrum, such as, for example, violet (400 nm), blue (475 nm), cyan(485 nm), green (510 nm), yellow (570 nm), orange (590 nm), and red (650nm). Other absorbed colors are also possible, including black.

Similarly, individual nanowires of the array may be fabricated to absorblight in at least one wavelength of various bands of the IR spectrum,such as, for example, near-infrared (NIR), short-wavelength infrared(SWIR), mid-wavelength infrared (MWIR), long-wavelength infrared (LWIR)or far infrared (FIR).

In one implementation, a plurality of nanowire arrays may also beconfigured for multispectral imaging or hyperspectral imaging, whichdetect electromagnetic (light) over multiple discrete spectral bandsand/or spectra (e.g., VIS, NIR, SWIR, MWIR, LWIR, FIR, etc). Thenanowire arrays may be configured for spectral-selective imaging whichdetect one or more specific wavelength of electromagnetic radiation(light). In one embodiment, an image sensor may be fabricated from anarray of nanowires with one or more nanowires forming each pixel of thesensor.

FIGS. 1A-1G are scanning electron microscope (SEM) images showingnanowire arrays of various diameters, according to an embodiment.

Vertical nanowire or nanopillar arrays may be fabricated, for example,by a dry etch method. Although, it will be appreciated that thenanowires may similarly fabricated using a VLS growing method, or otherfabrication techniques. The nanowires may be formed in a Cartesian (x-y)matrix structure so that each nanowire can be controlled or individuallyaddressed.

As shown, the nanowire arrays may be fabricated to have a very uniformcircular cross-sectional shape, for instance, of about 1 to 3 μm inlength or more. Using the VLS growing method, nanowires 10 μm in lengthcan be grown. Longer nanowires may be able to absorb more radiation asthey have a larger volume for the same given diameter. In addition, itmay be possible to confine more radiation for absorption, for instance,using a cladding material deposited around the nanowires.

Each of the arrays shown includes nanowires formed from silicon havingthe same diameters ranging from about 90 to 150 nm. This diameter rangemay be effective for absorbing various wavelengths (colors) of visiblelight. Of course, the nanowire diameters may need to be smaller forabsorbing wavelengths of UV light or larger for absorbing wavelengths ofIR light.

The size of each of the array may be about 100 μm×100 μm, having 10,000nanowires at a pitch (spacing) of about 1 μm or less in the x- and y-directions (in a Cartesian plane). Of course, the nanowire arrays may befabricated in larger sizes, for instance, having a million or morenanowires. The nanowires may be spaced apart at different (larger)intervals and/or forming different shapes, as well.

FIG. 2 shows a plot of reflectance spectra for nanowires havingdifferent diameters, but having the same pitch, according to anembodiment.

The measured reflectance spectra were obtained using a collimated lightmethod to measure reflectance of light from the nanowire array. Thereflectance was normalize with respect to a silver (Ag) mirror. For eachnanowire diameter, there is a significant dip in reflectance at aparticular wavelength. This reflectance dip corresponds to absorption oflight at that particular wavelength.

The bandwidth of the reflectance dip (or peak in absorption) isapproximately 50-100 nm at the particular wavelength.

FIGS. 3A-3C show experimental and simulated results for reflection of Sinanowire arrays, according to an embodiment.

FIG. 3A shows similar experimental results shown in FIG. 2, but themeasured reflectance spectra were obtained using a Raman spectroscopysetup configured to measure reflectance of light focused onto thenanowire array. The reflectance was normalized with respect to a silver(Ag) mirror. For each nanowire diameter, there is a significant dip inreflectance at a particular wavelength. This reflectance dip correspondsto absorption of light at that particular wavelength.

FIG. 3B shows simulated results. The computer-simulated results wereobtained by finite difference time domain (FDTD) simulations.

In this case, two different mathematical techniques for solvingMaxwell's equations were employed. The first employs a technique ofnumerically solving for the optical modes (eignenvalues and eigenmodes)of the nanowire array. The second numerical technique employed the FDTDapproach wherein a simulated illuminant is propagated through thenanowire array. The FDTD technique is a grid-based numerical modelingmethod in which time-dependant Maxwell's equations (in partialdifferential form) are discretized using central-differenceapproximation to the space and time partial derivations. The resultingfinite-difference equations for the electric field vector components aresolved at a given instance in time, and then the magnetic field vectorcomponents are solved in the next instance of time. This processing isrepeated over and over until a steady-state behavior is evolved.

There is a strong correlation between the dip position for reflectanceand the diameter of the nanowires for both the experimental andsimulated results. Although, for small diameter nanowire (e.g., lessthan about 200 nm), the simulation appears to indicate a single modeconfinement.

FIG. 3C more clearly shows the correlation between the dip positions andnanowire diameter for the experimental results and the simulationresults. There is a nearly linear correlation between nanowire diameterand the wavelength for the spectral dip position for reflectance (or thepeak for absorption) for the nanowire.

Experimental data appears to confirm that for certain nanowire spacingthe relationship is linear, especially for silicon nanowires. However,without being bound by theory, the inventors do not rule out thepossibility of non-linear effects that are small in magnitude and/orthat might have a larger impact using different materials or underdifferent fabrication conditions. Simulation, for example, shows thatfor larger diameter nanowires (greater than about 200 nm), if thespacing is too close, that there may be multimode coupling. As such, therelationship might not be linear.

FIG. 4 shows a plot of absorption spectra of Si nanowire arrays,according to an embodiment. There is clearly a peak absorption for eachnanowire diameter, which corresponds to the spectral dip of reflectionshown in FIG. 2.

FIG. 5 shows a plot of reflection spectra of Si nanowire arrays,according to an embodiment. This plot shows reflectance spectrum fornanowires of a length of 3 μm, while in FIGS. 2 and 4, the reflectancespectra shown are for nanowires having a length of 1 μm.

Both nanowires of 1 and 3 μm lengths, generally showed a spectral dip inreflectance at the same wavelength for the same nanowire diameter.Although, for at least the smaller nanowire diameter of 100 nm, the 3 μmlength nanowire experienced a much larger dip in reflectance than the 1μm length nanowire. The larger length nanowires have a greater volume,which in turn results in higher radiation absorption.

FIG. 6 shows a plot of absorption spectra of Si nanowire arrays,according to an embodiment. This plots show a comparison of theabsorption spectrum for nanowires which are 1 μm and 3 μm in length.

Both nanowires of 1 and 3 μm lengths, generally showed an increase inabsorption at the same wavelength for the same diameter. However, thenanowires of 3 μm length all showed a significant increase over thenanowires of 1 μm in length.

FIG. 7 shows a plot of absorption and reflection spectra of Si nanowirearrays, according to an embodiment. This plot shows absorption andreflectance spectrum for nanowire arrays having nanowires of 1 μm inlength. As is apparent, the absorption and reflection are inverselycorrelated, with a dip in reflectance corresponding to a peak inabsorption at the same wavelength. The substrate also shows a similarphenomenon at the same wavelength. The dip in substrate absorption isactually due to the nanowire absorption at that wavelength (peak). Thisis atypical behavior for an ordinary silicon wafer.

FIG. 8 shows an exemplary dry etch method 800 for fabricating an arrayof vertical nanowires, according to an embodiment.

In step 801, a starting material is provided which may include a SOI(silicon on insulator) substrate with an intrinsic epi layer and n+ typelayer at the oxide interface. In one instance, the thickness of the i-layer and n+-layer may be 5 μm and 0.5 μm, respectively. In analternative implementation, the starting substrate may have a lightlydoped n-type epi-layer instead of the intrinsic epi-layer layer.

Next, in step 802, a shallow p+ type layer is formed by an ionimplantation with p-type dopant and minimum energy. Photoresist (PR) isdeposited on the p+ layer in step 803 for the preparation oflithography. And, in step 804, the PR is patterned, for instance, byemploying the electron beam (or e-beam) lithography technique.

Metal deposition commences in step 805, for example, by eitherevaporation or sputtering method. One metal that may be used in thefabrication, for example, is aluminum. A lift-off etch method is thenemployed in step 806 for removing the PR and any unwanted metal on it.

In step 807, a dry etch is performed using the metal pattern as a etchmask. For applying the dry etch on the silicon material, etching gasessuch as, for instance, octafluorocyclobutane (C₄F₈) and sulfurhexafluoride (SF₆) can be used. An array of circular pillars (nanowires)are formed by the etch process. The diameter of the etch mask determinesthe diameter of the pillars which form each nanowire. In oneimplementation, the etch mask may be formed of aluminum.

Since the surfaces of the etched pillars may be rough, a surfacetreatment may be needed to make surfaces smooth. Thus, in step 808, thepillar surfaces may be dipped briefly in an etchant, such as, potassiumhydroxide (KOH) and a cleaning performed afterwards.

In some embodiments, a readout circuit may further be fabricated inconnection with to the n+ layer, to control and individually addresseach nanowire in the array. The readout circuit may include a pluralityof switching transistors, with one or more switching transistorsprovided for selectively controlling or addressing each nanowire.

FIG. 9 shows an exemplary VLS method 900 for fabricating an array ofvertical nanowires, according to an embodiment.

In step 901, a starting material is provided which may include a SOI orSG substrate with an n+ type layer on top of the SiO₂. Next, in step902, PR is deposited for the preparation of the lithography. The PR maypatterned in step 903, for instance, by employing the electron beamlithography technique. Metal deposition commences in step 904 by eitherevaporation or sputtering method. Metals that may be used in thefabrication are gold or aluminum. In step 905, a lift-off etch method isemployed for removing the PR and any unwanted metal on it.

Continuing to step 906, intrinsic type nanowires are grown employing aVLS method. In an alternative embodiment, lightly doped n-type nanowirescan be grown instead of the intrinsic nanowires. The diameter of themetal mask (applied in step 904) determines the diameter of the pillarswhich form each nanowire grown ins step 906. In a subsequent step (notshown), a CMP technique may be employed to planarize the top surface andremove the metal.

In some embodiments, a readout circuit may further be fabricated inconnection with to the n+ layer, to control and individually addresseach nanowire in the array. The readout circuit may include a pluralityof switching transistors, with one or more switching transistorsprovided for selectively controlling or addressing each nanowire.

FIG. 10 shows a schematic of an image sensor 1000 in accordance with anembodiment.

The image sensor 1000 generally includes foreoptics 1010, an array ofpixels 1020, a readout circuit (ROC) 1030, a processor 1040 and adisplay device 1050. A housing 1005 may incorporate one of more theforegoing elements of the sensor 1000, and protects the elements fromexcessive/ambient light, the environment (e.g., moisture, dust, etc.),mechanical damage (e.g., vibration, shock), etc.

Electromagnetic radiation (light) L from a scene S emanates toward theimage sensor 1000. For clarity, only light L from the scene S impingingupon the sensor 1000 is depicted (although it will be appreciated thatlight L from the scene S radiates in all directions).

The foreoptics 1010 may be configured to receive the electromagneticradiation (light) L from the scene S and focus or collimate the receivedradiation onto the array of pixels 1020. for instance, foreoptics 1010may include, for instance, one or more of: a lens, an optical filter, apolarizer, a diffuser, a collimator, etc.

The array of pixels 1020 may be fabricated from an array of one or morenanowires, as disclosed above (see FIG. 8 or 9). Each of the pixels mayinclude one or more nanowires having a diameter that corresponds to apredetermined wavelength of electromagnetic radiation (light) L forabsorption by the sensor 1000. At least one of the nanowires in thearray may have a different determined diameter than another of thenanowire in the array. This enables multiple wavelength absorption (anddetection).

The ROC 1030 may be connected to the array of pixels 1020 and isconfigured to receive output from the pixels 1020. The ROC 1030 mayinclude one or more switching transistors connected to the nanowires forselectively controlling or addressing each pixel of the array 1020.

The processor 1040 is configured to receive output from the ROC 1030 andgenerate an image for viewing on the display device 1050. The processor1040 may, in some instances, be configured to provide data scaling,zooming/magnification, data compression, color discrimination,filtering, or other imaging processing, as desired.

In one embodiment, the processor 1040 may include hardware, such asApplication Specific Integrated Circuits (ASICs), Field ProgrammableGate Arrays (FPGAs), digital signal processors (DSPs), or otherintegrated formats. However, those skilled in the art will recognizethat the processor 1040 may, in whole or in part, can be equivalentlyimplemented in integrated circuits, as one or more computer programshaving computer-executable instructions or code running on one or morecomputers (e.g., as one or more programs running on one or more computersystems), as one or more programs running on one or more processors(e.g., as one or more programs running on one or more microprocessors),as firmware, or as virtually any combination thereof, and that designingthe circuitry and/or writing the code for the software and/or firmwarewould be well within the skill of one skilled in the art in light ofthis disclosure. In addition, those skilled in the art will appreciatethat the mechanisms of the subject matter described herein are capableof being distributed as a program product in a variety of forms, andthat an illustrative embodiment of the subject matter described hereinapplies regardless of the particular type of computer-readable mediumused to actually carry out the distribution.

The display device 1050 may include any device configured for displayingimage data. Exemplary displays may include a cathode ray tube (CRT),plasma, liquid crystal display (LCD), light emitting diode (LED)display, pen chart, etc. In some instance, the display device 1050 may,alternatively or additionally, include a printer or other device forcapturing the displayed image. In addition, the image data may be outputto an electronic memory (not shown) for storage.

In some implementations, the image sensor 1000 may be configured as aspectrophotometer to measure intensity of reflection or absorption atone more wavelengths.

In other implementations, the image sensor 1000 could be configured as aphotovoltaic device. By adjusting the spacing of the nanowires, it maybe possibly to nearly control all various wavelengths of a spectrum,without any reflection.

FIG. 11 shows a method 1100 for selectively imaging, according to anembodiment.

In step 1110, electromagnetic radiation (light) may be received, forinstance, using the image sensor 1000 (FIG. 10). Next, in step 1120, thearray 1020 of the image sensor 1000 may selectively absorb at least onepredetermined wavelength of electromagnetic radiation (light). Method1100 may be used for multispectral imaging or hyperspectral imagingapplications.

Depending on the construction of the nanowire array, multiplewavelengths of electromagnetic radiation (light) may be absorbed and/ordetected by selectively providing nanowires of different diameters. Athree-nanowire pixel element may be fabricated. Of course, pixels havingadditional nanowires are also possible.

FIG. 12 shows an exemplary pixel 1200 formed of three nanowires R, G, Bhaving different diameters configured to absorb red, green, and bluelight, according to an embodiment. For instance, the R, G, B nanowirescan have diameters configured to absorb wavelengths of about 650 nm, 510nm, and 475 nm, respectively (see, e.g., FIG. 3C).

An array can be fabricated from a plurality of pixels 1200. In oneimplementation, the effective diameter D of the pixel 1200 may be 1 μmor less. A cladding 1210 may, in some instance, surround the pixel 1200to increase absorption of the nanowires.

The foregoing detailed description has set forth various embodiments ofthe devices and/or processes by the use of diagrams, flowcharts, and/orexamples. Insofar as such diagrams, flowcharts, and/or examples containone or more functions and/or operations, it will be understood by thosewithin the art that each function and/or operation within such diagrams,flowcharts, or examples can be implemented, individually and/orcollectively, by a wide range of hardware, software, firmware, orvirtually any combination thereof.

Those skilled in the art will recognize that it is common within the artto describe devices and/or processes in the fashion set forth herein,and thereafter use engineering practices to integrate such describeddevices and/or processes into data processing systems. That is, at leasta portion of the devices and/or processes described herein can beintegrated into a data processing system via a reasonable amount ofexperimentation.

The herein described subject matter sometimes illustrates differentcomponents contained within, or connected with, different othercomponents. It is to be understood that such depicted architectures aremerely exemplary, and that in fact many other architectures can beimplemented which achieve the same functionality. In a conceptual sense,any arrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality isachieved. Hence, any two components herein combined to achieve aparticular functionality can be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermediate components.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations may be expressly set forth herein for sakeof clarity.

All references, including but not limited to patents, patentapplications, and non-patent literature are hereby incorporated byreference herein in their entirety.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

What is claimed:
 1. A nanowire on a substrate, comprising the nanowireand the substrate, wherein: the nanowire has a determined diameter;wherein the determined diameter corresponds to a particular wavelengthof electromagnetic radiation for absorption of the nanowire; wherein thenanowire is essentially vertical to the substrate;. wherein the nanowirewith the determined diameter has an absorption peak of electromagneticradiation at the particular wavelength.
 2. The nanowire according toclaim 1, wherein the diameter of the nanowire is between about 90 and150 nm for absorbing electromagnetic radiation in the visible spectrum.3. The nanowire according to claim 2, wherein the length of the nanowireis between about 1 and 10 μm.
 4. The nanowire according to claim 3,wherein the bandwidth of the particular wavelength of absorption isapproximately 50-100 nm.
 5. The nanowire according to claim 4, furthercomprising a cladding material deposited around the nanowire.
 6. Adevice comprising a plurality of pixels, each of the pixels including atleast one nanowire of claim
 1. 7. The device according to claim 6,wherein at least one of the nanowires in the array has the same or adifferent determined diameter than another of the nanowires in thearray.
 8. The device according to claim 7, wherein the at least one ofthe nanowires in the array has a different determined diameter thananother of the nanowire in the array.
 9. The device according to claim8, wherein each pixel has a plurality of nanowires, and at least one ofthe nanowires in the pixel has a different determined diameter thananother of the nanowires in the pixel.
 10. The device according to claim9, wherein there are three nanowires in each pixel.
 11. The deviceaccording to claim 10, wherein the three nanowires are configured toabsorb red, green and blue light, respectively, in the visible spectrum.12. The device according to claim 6, further comprising foreopticsconfigured to receive the electromagnetic radiation and focus orcollimate the receive radiation onto the one or more pixels.
 13. Thedevice according to claim 6, further comprising a readout circuitconfigured to receive output from the one or more pixels.
 14. The deviceaccording to claim 13, further comprising a processor configured toreceive an output from the readout circuit and generate an image. 15.The device according to claim 14, further comprising a display deviceconfigured to display the image generated by the processor.
 16. Thedevice according to claim 6, wherein the device is configured as aspectrophotometer or as a photovoltaic device.
 17. The device accordingto claim 6, wherein the device is configured as an image sensor.
 18. Amethod of imaging comprising receiving electromagnetic radiation; andselectively absorbing, via the device of claim 6, the particularwavelength of the electromagnetic radiation.
 19. The method according toclaim 18, further comprising performing multispectral imaging orhyperspectral imaging.
 20. The method according to claim 18, furthercomprising detecting multiple wavelengths of electromagnetic energyusing nanowires having different diameters.